1. Field of the Invention
The present invention relates to a pixel defect detector which is provided in a solid-state imaging device such as a CCD for automatically detecting a defect produced in the solid-state imaging device.
2. Description of the Related Art
It is generally known in the art that the quality of a solid-state imaging device such as a CCD may deteriorate due to a local crystal defect (also referred to as a “blemish”) which is produced therein while being manufactured. Moreover, an additional blemish may be produced in the solid-state imaging device after shipping by the irradiation of cosmic rays. Such blemishes can be classified into white blemishes and black blemishes.
FIG. 6 shows a graph illustrating output characteristics in response to the amount of incident light of different photoelectric transducers (referred to also as “pixels”) provided in a solid-state imaging device. In FIG. 6, the solid line A represents an output characteristic of a normal pixel, the broken line B represents that of a pixel having a white blemish, and the one-dot chain line C represents that of a pixel having a black blemish. As can be seen from the output characteristic represented by the broken line B, a white blemish is a defect due to which a bias voltage is always added to an output of the pixel. Moreover, as can be seen from the output characteristic represented by the one-dot chain line C, a black blemish is a defect by which the sensitivity of the pixel is reduced.
Conventionally, various devices and methods have been proposed in the art for detecting such a blemish in a pixel and correcting the output of such a pixel.
For example, Japanese Laid-Open Publication No. 8-195909 discloses an arrangement comprising: a ROM for storing data representing the position and the level of a CCD blemish which is already present prior to shipping; and an EEPROM for storing data representing the position and the level of a CCD blemish which is additionally produced after the shipping. According to this arrangement, the output of the CCD having a blemish is corrected based on the data stored in the ROM and the data stored in the EEPROM.
Japanese Laid-Open Publication No. 7-7675 discloses a technique in which a blemish of a CCD is detected after performing an inverse γ correction on an output signal of the CCD. The inverse γ correction is performed because once a γ correction is performed, the amount of error occurring in the output signal of the CCD due to the blemish is reduced, whereby the blemish detection is difficult.
Japanese Laid-Open Publication No. 62-8666 discloses a technique of substituting the output signal of a pixel having a blemish with the output signal of another pixel in the same row or column.
In the prior art, however, the detection of a blemish in a solid-state imaging device either before or after shipping requires a reference light generator for producing various (dark to bright) levels of reference light incident upon the device, an aided system, and the like. Moreover, in the prior art, the detection of a blemish in a pixel and the correction of the output from the pixel may be difficult for anyone but an expert operator. These operations are far from those which can ordinarily be done by a user.